With the advent of computer controlled digital imaging techniques such as ink-jet or electrophotographic printing, it is now possible to mass-produce individualized printed copies. This has created many new markets for these imaging technologies. For example, labeling, bar coding, targeted advertising, and even individualized book publishing are now performed in this manner as opposed to standard printing techniques. Although this has obvious advantages for legitimate business, the same technology also allows for its misuse by permitting unauthorized duplication of original documents for the purpose of passing them off as original documents. For example, these imaging techniques have been used to generate false identity cards or counterfeit currency. To ensure valid, authentic documentation, additional security devices must be employed that will prevent accurate reproduction of original documentation so falsified documents can easily be detected either by eye or with low cost reading technologies.
Many types of identification cards and documents, such as driving licenses, national or government identification cards, bank cards, credit cards, controlled access cards and smart cards carry information relating to the identity of the bearer. The most important items of information are name, address, birth date, signature and photographic image. Additionally, the cards or documents may carry other variant data (i.e., data specific to a particular card or document, like an employee number, for example) and invariant data (i.e., data common to a large number of cards, like the name of an employer). All of the cards described above will hereinafter be generically referred to as “identification documents.”
Commercial systems for issuing identification documents are of two main types, namely “on-the-spot” or “over-the-counter” (OTC) issue, and “central” issue. As the name implies, the former are issued immediately to a bearer who is present at a document-issuing station, whereas with the latter type, a bearer reports to a document station where data is collected, the data are forwarded to a central location where the card is produced, and the card is forwarded to the bearer, often by mail.
Centrally issued digital identification documents generally comprise an opaque laser or ink-jet printed core material, typically either paper or plastic, sandwiched between two layers of clear plastic laminate, typically polyester, to protect the aforementioned items of information from wear, exposure to the elements and tampering. The materials used in such centrally issued digital identification documents can offer the ultimate in durability. In addition, centrally issued digital identification documents generally offer a higher level of security than digital OTC identification documents because they have the ability to pre-print the laser or ink-jet printed core of the central issue document with “micro-printing,” ultra-violet security features, security indicia, and other features currently unique to centrally issued identification documents.
The use of ink-jet technology to produce essentially permanent customized images for identity cards would seem to have potential, but several problems have remained. In particular, ink-jet imaged products have not provided highly water resistant or waterproof characteristics. Furthermore, ink-jet inks are prone to fade with time. Also, lamination of such products typically has caused image alteration due to melting of the image-receiving layer. Another limitation of the present protection technology is that delamination can be effected without destroying the image and therefore permitting modification or falsification of information.
Furthermore, it has been a general long-standing problem in the art to provide a recording sheet for ink-jet printing which is receptive to inks, allows the ink to dry quickly without running or smearing, provides sharp image quality and has very good water and humidity resistance which deters curling. Many attempts have been made to produce recording sheets for ink-jet printing which simultaneously have all of these properties.
U.S. Pat. No. 4,371,582, issued to Sugiyama et al. on Feb. 1, 1983 for INK-JET RECORDING SHEET describes an ink-jet recording sheet containing a basic latex polymer. U.S. Pat. No. 3,158,494, issued to Elkvar et al. on Nov. 24, 1964 for COATED POLYMERIC THERMOPLASTIC SHEET MATERIAL describes a polyurethane ink receptive surface. U.S. Pat. No. 5,693,410, issued to Malhotra et al. on Dec. 2, 1997 for INK-JET TRANSPARENCIES describes ink-jet recording transparencies having two coatings, namely a heat dissipating, fire resistant coating in contact with a substrate and a second ink receiving coating layer on the first layer comprising a hydrophilic binder, an ink spreading agent, a cationic component, a light-fastness inducing agent, a filler and a biocide. JP Pat. 92/02,041 describes ink-jet recording media having good ink drying properties comprising a substrate provided with at least one ink receiving layer which contains a reaction product of polyalkylene oxide with an isocyanate and a water insoluble cellulose compound. While the above ink-jet media may be suitable for intended purposes, there remains a need for a universal ink-jet media for a dye based ink system as well as a pigment based ink system. Further, there is a need for a universal ink-jet media useful for obtaining photographic quality prints by both thermal and piezo ink-jet printing technologies. Additionally, there remains a need for coatings for ink-jet media which have good water resistance and which can counter media curl due to humidity changes.
With regard to water resistance, significant effort has been expended on improving either the ink systems or the recording medium to achieve an image that will possess superior water resistance. Due to the interaction of the ink with the image-receiving layer it was not uncommon to create dedicated ink/substrate systems. Typically, one of the major advantages of the ink-jet imaging process is that the dyes employed are mainly water-soluble. Therefore, the system requires little or no organic solvent and is mainly water-based or aqueous media thereby creating a system that is environmentally friendly. However, this presents a significant design problem if, on the other hand, water resistance is required for the final imaged article. Inks utilizing pigments have been used to alleviate this problem since the pigments themselves are not water soluble and therefore after imaging will not run or bleed. However, the pigment particles generally, will not be absorbed into the image receiver layer, but rather reside on its surface and therefore can be easily removed by physical abrasion.
In U.S. Pat. No. 6,225,381, issued to Sharma et al. on May 1, 2001 for PHOTOGRAPHIC QUALITY INK-JET PRINTABLE COATING ink-jet printable-coated media that overcome the above-noted disadvantages the invention provides coating compositions that, when applied to suitable substrates such as transparent, translucent, or opaque white plastic films, paper, or the like, can achieve photographic quality prints by using any of a variety of ink-jet printers. The coating composition is compatible with dye based and pigment based ink systems, which can be printed both by thermal type ink-jet printers and piezo type ink-jet printers.
In U.S. Pat. No. 5,494,960, issued to Rolando et al. on Feb. 27, 1996 for AQUEOUS POLYURETHANE DISPERSIONS AND ADHESIVES BASED THEREON, aqueous polyurethane dispersions having anionic moieties which can be used in adhesives for manufacturing laminate structures with improved dispersion properties, which provide improved shelf-life stability of the dispersion and greater transparency and handling characteristics in application machinery for adhesives formulated therefrom, when a tertiary amine is present during an initial polyurethane prepolymer reaction between an isocyanate and a polyol component having acid functional groups are reported. The initial reaction is carried out prior to formation of the dispersion in water.
Polyurethanes having anionic moieties have been reported in U.S. Pat. No. 5,691,425, issued to Klein et al. on Nov. 25, 1997 for POLYURETHANE DISPERSIONS. Klein et al. disclose that their inventive polyurethane dispersions are suitable for diverse uses, for instance, in the preparation of coating systems, inter alia for coating wood, as binders for water-dilutable adhesives or as resins for printing inks.
Nakamura et al., in U.S. Pat. No. 5,470,818, issued on Nov. 28, 1995 for PRINTING SHEET COMPRISING A DYE RECEIVING LAYER MADE OF AN ISOCYANATE GROUP-CONTAINING POLYMER and U.S. Pat. No. 5,470,817, issued on Nov. 28, 1995 for PRINTING SHEET AND MANUFACTURING METHOD THEREFOR, report a printing sheet adapted for use in thermal transfer recording comprising a substrate (1) and a dye image-receiving layer (2) formed on the substrate. The layer (2) comprises an isocyanate group-containing polymer having at least one polysiloxane moiety and at least one urethane bond site therein. The isocyanate group-containing polymer is a reaction product between polyfunctional polyisocyanate compound and alcohol-modified silicone. A method for making such a sheet is also described. However, Nakamura et al. are concerned with optimizing a thermal ink receiving sheet that has low smearing by hand and acceptable writability. No mention is made of the need or desire to laminate this imaged material.
In U.S. Pat. No. 5,022,947, both issued to Hasegawa et al. on Jun. 11, 1991 for METHOD FOR THE PREPARATION OF A WATER-RESISTANT PRINTED MATERIAL, and U.S. Pat. No. 4,966,804, issued on Oct. 30, 1990 for PRINTED MATERIAL IMPARTED WITH IMPROVED WATER-PROOFNESS, a means to prepare a highly water-resistant printed material by the ink-jet printing method despite the water-solubility of the dye in the aqueous ink used in the ink-jet printing method is reported. The inventive method comprises overcoating the surface of the sheet material, which has a water-absorptive surface layer with receptivity of the aqueous ink and printed by the ink-jet printing method, with a curable polyisocyanate compound and bringing the overcoating layer under a condition capable of curing the polyisocyanate compound. This patent makes no reference to laminating the isocyanate layer to any other material. Rather the intent is to harden or cure the isocyanate to improve waterfastness.
In U.S. Pat. No. 4,578,285, issued to Michael S. Viola on Mar. 25, 1986 for INK-JET PRINTING SUBSTRATE, a printing substrate adapted to receive ink droplets to form an image generated by an ink-jet printer which comprises a transparent support carrying a layer comprising at least 70 weight percent polyurethane and 5 to 30 weight percent of a polymer selected from the group consisting of polyvinylpyrrolidone, polyvinylpyrrolidone/vinyl acetate copolymer, poly (ethyleneoxide), gelatin and polyacrylic acid is reported. No mention is made of subsequent lamination.
It is a general practice in conventional xerography to form electrostatic latent images on a xerographic surface by first uniformly charging a charge retentive surface such as a photoreceptor. The charged area is selectively dissipated in accordance with a pattern of activating radiation corresponding to original images. The selective dissipation of the charge leaves a latent charge pattern on the imaging surface corresponding to the areas not exposed by radiation.
This charge pattern is made visible by developing it with toner by passing the photoreceptor past one or more developer housings. In monochromatic imaging, the toner is generally comprised of black thermoplastic powder particles that adhere to the charge pattern by electrostatic attraction. The developed image is then fixed to the imaging surface or is transferred to a receiving substrate such as plain paper to which it is fixed by suitable fusing techniques.
The quality of color xerographic images on paper has approached the quality of color photographic prints. However, color xerographic prints fall short because they do not have the uniform gloss, dynamic range, or brilliance typical of photographic prints. Furthermore, xerographic prints do not have the feel of photographic prints because the paper used is usually too lightweight and limp.
Also the surface of color toner images is typically irregular, therefore providing a rather rough or lumpy appearance. The behavior of incident white light vis-a-vis such color images is believed to be as follows: some of the white light incident on the substrate carrying the color toner images specularly reflects off the substrate. Some of the light goes into the paper, scatters around, and comes back out in various directions. Some comes through the toner and some does not. Because the toner surface is rough or irregular some of the light incident thereon is reflected off the toner in various directions. Some of the light incident on the irregular toner surfaces passes through the toner into the paper and comes back out in various directions. White light becomes colored due to selective absorption as it passes through toner. The light then goes into the paper and back out through the toner whereby it becomes more colored through more absorption. Any white light that does not pass through the toner diminishes the appearance of the final print.
Attempts to make up for this deficiency in conventionally formed color toner images have led to the lamination of xerographic images on paper using a transparent substrate. This procedure has only been partially successful because the lamination process tends to reduce the density range of the print, resulting in a print that has less shadow detail. The lamination process also adds significant weight and thickness to the print.
Additionally, it is believed that the aforementioned lamination process does not produce good results because the color toner images at the interface between the laminate and the toner typically do not make suitable optical contact. That is to say, the initially irregular toner image at the interface is still irregular enough after lamination (i.e., contains voids) that light is reflected from at least some of those surfaces and is precluded from passing through the toner. In other words, when there are voids between the transparency and toner image, light gets scattered and reflected back without passing through the colored toner. Loss of image contrast results when any white light is scattered, either from the bottom surface of the transparent substrate or from the irregular toner surfaces and does not pass through the toner.
Digital OTC identification documents of the types mentioned above generally comprise highly plasticized poly (vinyl chloride) or have a composite structure with polyester laminated to highly plasticized 0.5–2.0 mil (13–51 μm) poly(vinyl chloride) film, which provides a suitable receiving layer for heat transferable dyes which form a photographic image, together with any variant or invariant data required for the identification of the bearer. These data are subsequently protected to varying degrees by clear, thin (0.125–0.250 mil, 3–6 μm) overlay patches applied at the printhead, holographic hot stamp foils (0.125–0.250 mil, 3–6 em), or a clear polyester laminate (0.5–10 mil, 13–254 μm) supporting common security features; these last two types of protective foil or laminate are applied at a laminating station separate from the printhead. The choice of laminate dictates the degree of durability and security imparted to the system in protecting the image and other data. Although such OTC documents are in wide use throughout the world, they suffer from several disadvantages. Both the highly plasticized poly(vinyl chloride) type and the polyester/poly(vinyl chloride) composite type become embrittled over time because of migration of the plasticizers, thus reducing the resistance of the document to cracking. Such cracking renders the card unusable and vulnerable to tampering.
The data described above which are crucial to the identification of the bearer are often covertly repeated on the document in encrypted form for data verification in a magnetic stripe, bar code, radio frequency module, or integrated circuit chip. The inability to retrieve such data due to cracking renders the document invalid. In addition, many of the polyester/poly(vinyl chloride) composite documents have exhibited extreme sensitivity to combinations of heat and humidity, as evidenced by delamination and curling of the document structure.